1. Field of the Invention
The invention disclosed herein is concerned with the emergency steering systems of hydraulically steered vehicles. Particularly emphasized is the method of initiating the emergency steering function.
2. The Description of the Prior Art
The usual method for steering large construction vehicles is through the use of hydraulic steering. Vehicles such as articulated tractors, articulated loaders, road graders and off the road trucks are included in this group of large vehicles.
In hydraulic steering systems on this type of equipment the vehicle engine is usually geared to drive a positive displacement, either fixed or variable, hydraulic pump which supplies fluid to the steering cylinders. An open center valve arrangement may be incorporated in the system to direct fluid to the appropriate steering cylinder or back to a fluid reservoir when fluid flow to the steering cylinders is not needed.
In an emergency situation, such as an engine failure or the steering system hydraulic pump failure, a vehicle having a hydraulic steering system would loose steering control as the flow of fluid to the steering cylinders is paramount to the operation of the system.
Various solutions have been proposed to provide fluid flow to the steering systems when a system component fails. Typically either an accumulator is used to store fluid under pressure for use as necessary or a ground drive auxiliary pump is incorporated into the steering system. Also, auxiliary power sources such as electric motors have been provided to drive hydraulic pumps.
An accumulator proves to be deficient as it can only supply a limited amount of fluid for a limited time. Thus emergency steering will be inoperative upon exhaustion of the fluid from the accumulator. The electrically driven pump has the advantage of being available at all times to supply fluid flow to the steering system. However, it is desirable to have this pump operating only during times of need.
An emergency steering system incorporating a ground drive pump is the most effectual of present systems. A ground drive pump incorporating the innovations of the present invention will be very efficient in operation.
A significant innovation of the present invention is the sensing system which allows the engagement of the ground drive pump upon loss of fluid pressure from the primary system.